1. Field of the Invention
The present invention relates to a method of and an apparatus for correcting a color in accordance with the hue, lightness, and saturation of a color signal.
2. Description of the Related Art
In the art of printing and platemaking, there have widely been used image reading, recording, and reproducing systems for electrically processing image information read from original images to produce film plates in order to make printing and platemaking processes more efficient and improving the quality of images reproduced from such film plates.
In such an image reading, recording, and reproducing system, it has been customary to use a color correction circuit to determine the hue of a color signal produced when an original image is scanned and correct the color represented by the color signal for the purposes of making clear colors of a reproduced image and removing color impurities therefrom. To make clear colors of a reproduced image, the number of necessary colors may be increased, and to remove color impurities, unwanted colors may be eliminated.
The conventional color correction circuit decides the hue of an input signal from the magnitudes of the three color signals of C, M, Y of the input signal, determines which one of six hues of C, M, Y, B, G, R the decided hue belongs to, and produces a corrective quantity by multiplying, by a corrective coefficient, a reference quantity that is given as a saturation or intensity with respect to the determined hue.
According to the above process of producing a corrective quantity, the calculated hue may possibly differ from the actual hue which the human eye visually recognizes, possibly resulting in the correction of a color which is not intended. Furthermore, since the saturation as the reference quantity is obtained as the density difference between two color signals, the same corrective quantity is produced for light colors and dark colors whose density differences are the same. If the corrective quantity for the dark colors are to increase, then the contrast of the light colors will be increased, with the result that an image which will be reproduced based on those color signals is unnatural to the eye.
To avoid the above drawback, it may be effective to correct the corrective quantity using a function dependent on the lightness. According to such a correcting scheme, however, if the corrective quantity for light colors is to be suppressed, then dilute colors, which have a high lightness but a low saturation, cannot be sufficiently corrected.